The invention relates to a lens shutter mechanism for a camera, or more particularly, to a lens shutter mechanism for a camera which opens and closes shutter blades, which also serve as diaphragm blades.
As is well recognized, there is a lens shutter of semi-open type which includes shutter blades also serving as diaphragm blades and begins to drive in a closing direction before the shutter blades reach their fully open position. Such a lens shutter makes it possible to definitely determine the the proper combination of shutter speed and diaphragm aperture in accordance with the brightness of an object being photographed. Consequently, it generally adopts a programmed exposure control scheme.
A conventional lens shutter of such programmed exposure control type, hereafter referred to as a program shutter, generally utilizes an electromagnet in order to maintain the shutter blades in their open condition. The electromagnet is effective to maintain a member, which is used to drive the shutter blades in their closing direction, in a position which corresponds to the fully open position of the shutter blades. Consequently, when a proper exposure of the film is reached before the shutter blades become fully open to cause the electromagnet to be deenergized, the member which drives the shutter blades in their closing direction initially moves from the position corresponding to the full open condition of the shutter blades to an intermediate position which corresponds to the proper exposure, followed by a closing operation of the shutter blades. This means that there is a delay from the time the proper exposure is reached until the closing operation of the shutter blades is initiated. Since the shutter blades remain open during this delay, there results an inconvenience such as an overexposure. A conventional shutter of the kind described has been incapable of accommodating for a changes in light received from an object being photographed which occurs during such delay, resulting in a poor accuracy of the exposure control. Such drawback is particularly remarkable during a high speed operation, as partly assisted by the complexity of the closing mechanism, resulting in a dissatisfactory operational stability.
Another disadvantage of a conventional program shutter is the incapability to serve as a diaphragm preset shutter assembly since the shutter blades are adapted to be operated by the release of a stored resilience, which prevents the shutter blades to be maintained in their semi-open condition.
In addition, the synchro contacts cannot be operated at an intermediate position of the shutter blades. This prevents a shutter operation as a so-called flashmatic shutter.
Furthermore, a conventional program shutter is of an ever-set type in which the drive to the shutter blades is derived from the resilience which is stored in response to the depression of a shutter release button. Consequently, such shutter suffers from an increased operating stroke of a shutter release member. Although a shutter is available in which the drive to the shutter blades is stored in connection with a film winding operation of a film winding mechanism, such shutter requires a connection with the film winding mechanism, resulting in a complex construction.
Where it is desired to provide a shutter of an electromagnetic release type, it is necessary to provide a release electromagnet, which requires an increased stroke for the member which operates the shutter.
Finally, a conventional program shutter generally employs an increased number of parts, requiring an increased space therefor.
On the other hand, a variety of distance adjusting mechanisms for camera are known in which a desired distance adjustment is achieved by driving a taking lens assembly by means of a drive motor. However, in the conventional mechanisms of this kind, the angular position of the drive motor has a definite or one-to-one correspondence to the distance focussed by the taking lens, and hence to maintain the taking lens at a selected distance, the drive motor must be held stationary at a corresponding angular position. Accordingly, the drive motor used in the distance adjusting mechanism must be provided as a devoted one, and cannot be utilized to operate a shutter, for example. Accordingly, when a full automation of the camera is contemplated, a plurality of motors must be provided within a camera, causing an increased size and increased cost thereof. Also, the plurality of motors must be sequentially controlled in accordance with a series of photographing operations, disadvantageously resulting in a complex control program utilized in a control circuit.